A new class of antibody found in the blood of patients with dengue fever has boosted hopes for a vaccine against the virus, which debilitates millions and kills tens of thousands each year.

Cases of dengue fever have soared in the past 50 years to nearly 100 million a year as improved transport and urbanisation have brought more people into contact with the mosquito-borne virus.

While dengue infection often causes mild to high fever and lasts only a week or so, some patients develop dengue haemorrhagic fever, which is far more serious and kills about 22,000 people a year, many of them children.

“The real problem with dengue is it occurs in an epidemic fashion, so it can paralyse healthcare systems when it comes through a big city, causing thousands of hospitalisations,” said Gavin Screaton at Imperial College, London.

“It’s likely that without a vaccine this disease is not going to be controlled,” he added.

The researchers spotted the new group of antibodies while they were studying blood drawn from patients who picked up dengue infections in south-east Asia.

They found that about a third of the immune reaction launched by each patient came from a new class of antibodies. Instead of latching on to a single protein on the virus surface – as usually happens – the new group of antibodies latches on to a molecular bridge that joins two virus proteins together.

When antibodies bind to viruses, they make them targets for attack from the wider immune system.

In tests described in the journal Nature Immunology, the researchers found that the newly identified antibodies were highly effective at fighting the dengue virus in mosquitoes and in patients. But more surprising, and useful for a vaccine, they also neutralised all of the different forms of the germ.

There are four different strains of dengue virus. When a person becomes infected, their body will become immune to that strain, but they are still vulnerable to infection from the other three. Reinfection with a second strain of dengue substantially raises the risk of developing serious dengue haemorrhagic fever.

The antibodies were effective against all four strains of the virus because they all share the molecular bridge the antibodies attach to.

In follow-up work reported in the study, the scientists went on to manufacture a batch of the human antibodies. Once they have cleared trials, these could be used to treat dengue fever, or administered to protect people against the virus.

But another approach is to synthesise the virus’s molecular bridge in a form that can itself be used in a vaccine. Such a vaccine would protect against the infection by training the immune system to recognise the bridge and so attack any virus as soon as it enters the body.

About 2.5 billion people – more than a third of the world’s population – live in areas where dengue infection is a risk. The virus is endemic in at least 100 countries in the Americas, Africa, Asia, the Pacific and the Caribbean.